查看更多>>摘要：The SiBCN composite fibers with strong electromagnetic wave (EMW) absorption performance were successfully prepared via polymer-derived ceramics (PDCs) and electrospinning methods at relatively lower preparation temperature. The results showed that the in-situ generated free carbon which existed in the matrix in the form of simple substance and was characterized by low crystallinity. The graphite carbon improved the dielectric loss and properties of SiBCN composite fibers. In particular for the SiBCN composite fibers pyrolyzed at 1300 degrees C, the in-situ generated nano beta-SiC crystallization increased the EMW absorption performance significantly. The minimum reflection loss (RLmin) of the SiBCN-3 reached - 54.91 dB at 2.35 mm and the effective absorption band (EAB, RL <= -10 dB) reached 4.72 GHz (13.28-18 GHz, 1.75 mm). Hence, the SiBCN fibers prepared at relatively lower temperature give good absorption performance and predict a broader application prospect in the field of EMW absorption materials.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Developing highly efficient strategy for fabrication of bifunctional electrocatalysts for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) is a challenging topic. In this work, we reported the in situ synthesis of N, S co-doped carbon nanorod material (N/S-C) by the facile template-free, one-step pyrolysis approach using N and S co-containing poly(ionic liquid) (PIL) of p[BZ][HSO4](2) as precursor derived from the simple chemically oxidative polymerization of ionic liquid benzidine sulfate ([BZ][HSO4](2)) in the presence of ammonium persulfate as oxidant. The N/S-C catalysts have nanorod morphology with hierarchical porous architectures of abundant micropores and well-defined mesopores featuring high specific surface areas. The ORR performance of N/S-C-800 is extremely satisfactory in alkaline media with the onset and half-potentials of 0.985 V and 0.857 V (vs. RHE), respectively, which are comparable to that of commercial Pt/C (0.990 V and 0.852 V vs. RHE). It also delivers the favorable long-term stability and methanol tolerance, significantly outperforming commercial Pt/C. Moreover, the N/S-C-800 was served as a support for Pt nanoparticles, showing the higher methanol electrooxidation activity (806.74 mA mg(Pt)(-1)) compared with commercial Pt/C (356.32 mA mg(Pt)(-1)). These results show an effective route to design the attractive metal-free carbon-based electrocatalysts for direct methanol fuel cells. (C) 2022 Elsevier B.V. All rights reserved.
Streltsov, Sergey V.Ryltsev, Roman E.Chtchelkatchev, Nikolay M.
6页
查看更多>>摘要：In recent years, A-site ordered half-doped double-perovskite manganites RBaMn2O6 (R=rare earth) have attracted much attention due to their remarkable physical properties and a prospect of application as magnetoresistive, multiferroic, and oxygen storage materials. The nature of the ground state in RBaMn2O6 as well as sequence of phase transitions taking place at cooling are not yet well understood due to complexity in both experimental and theoretical studies. Here we address the origin of the ground-state structure in PrBaMn2O6 as well as its electronic and magnetic properties. Utilizing GGA+U approach and specially designed strategy to perform structural optimization, we show that the system has two competing AFM-A and AFM-CE magnetic structures with very close energies. The AFM-A structure is a metal, while AFM-CE is an insulator and the transition to the insulating state is accompanied by the charge Mn3+/Mn4+, and orbital 3x(2) - r(2)/3y(2) - r(2) orderings. This orbital ordering results in strong cooperative Jahn-Teller (JT) distortions, which lower the crystal symmetry. Our findings give a key to understanding contradictions in available experimental data on PrBaMn2O6 and open up the prospects to theoretical refinements of ground state structures in other RBaMn2O6 compounds. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：High-performance metal-oxide thin-film transistors (oxide-TFTs) with high-k zirconium dioxide (ZrO2) dielectric and indium-gallium-zinc oxide (IGZO) semiconducting films were developed on flexible polyimide substrates. The flexible IGZO-TFTs fabricated using a simple and effective sol-gel-based solution -process combined with oxygen-enriched consecutive annealing at 200 & DEG;C, exhibited a high field-effect mobility of 13.6 cm(2) V-1 s(-1) at 5 V, on/off ratio of 1.05 x 10(6), gate leakage current of 2.7 x 10(-11) A, and threshold voltage of 0.44 V. The effects of O-2 annealing on the film quality of the sol-gel-based ZrO2 and IGZO were investigated by analyzing the crystallinity, morphology, and degree of metal-oxygen bonding states. Temperature-dependent steady-state direct-current measurements over the temperature range of 90-300 K, and time-domain non-quasi-static transient measurements with a minimized resistance-capacitance time constant were performed. Thus, the activation energy, density of states, interface trap density, and velocity distribution were determined to investigate the charge transport mechanism responsible for the high performance of the oxide-TFTs proposed in this study. An enhancement-load-type N-channel metal-oxide semiconductor (NMOS) inverter consisting of two oxide-TFTs fabricated via O-2 annealing was demonstrated. The flexible NMOS inverter exhibited a high gain of 10.8 at 5 V and outstanding mechanical stability against 10,000 cycles of bending stresses at a strain of 30% without a passivation or buffer film.(c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Equiaxed solidification contributes to the ridging defect resistance of ferritic stainless steel. Ti2O3 accelerating TiN formation to nucleate delta-ferrite was recently recognized as an effective method to promote equiaxed solidification. However, the acceleration mechanism of Ti2O3 is still unclear, and there lacks direct nucleation evidence. Therefore, in this study, the initial solidification state was preserved using a newly designed droplet experiment. The orientation relationship calibrated disregistry calculation was carried out to understand the nucleation phenomena. It is novel to find that the formation of Ti2O3-TiN originates from the Ti-O-N particle, which forms before solidification of steel. The sequenced precipitation in the order of Ti2O3 and TiN from the Ti-O-N particle follows the orientation relationship of {0001} Ti2O3 // {111} TiN and finally constitutes the Ti2O3-TiN. Afterward, the delta-ferrite nucleation will be promoted on the surface of the as-formed Ti2O3-TiN following {001} delta-Fe // {001} TiN. The primary delta-ferrite dendrite preserved in the droplet experiment affirmed the proposed mechanism. These findings will expand the knowledge of oxide accelerating nucleation and could contribute to suitable compositional design for equiaxed solidification. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Pure and Al-doped ZnO nanoparticles are synthesized by hydrothermal technique. The structural and phase analysis of the prepared powder is attained by X-rays diffraction and concluded that Al doping increases the crystallite size and causes compressive stress formation in the material network. Fourier transforms infrared spectroscopy reveals the formation of the aluminum oxide phase but with a tiny size that XRD cannot detect. The impact of different ratios of Al doping influence on powder morphology is carried out using transmission electron microscopy, and the optical bandgap of all synthesized products with the doping ratio is investigated by UV-visible reflectance. The electronic defects localized in the material band-gap are studied via photoluminescence spectroscopy and inferred that Al doping alters significantly the electronic defects nature present in the band-gap. In this study, the intrinsic oxygen vacancies are removed by replacing Zn when Al atoms are introduced into the material network. (C) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：In this work, Al-0.88Er-0.78Zr (wt%) alloy was fabricated via laser powder bed fusion (LPBF). The microstructure, precipitates distribution, electrical conductivity and hardness of as-built and aging treatment specimens were carefully characterized. Results show that LPBF process greatly expand the solid solubility of Er and Zr in Al. The addition of Er can significantly refine the grain size and form a bimodal grain structure consisting of fine equiaxed grains (grain size ~0.53 & PLUSMN; 0.15 mu m) at the boundary of molten pool together with coarse columnar grains (width 2.57 +/-& nbsp;0.84 mu m) at the center of molten pool. After 375 celcius for 3 h aging treatment, the particles on the grain boundary inhibit the grain growth; at the same time, a large number of Al3(Er,Zr) particles with L12 structure and size of 2.25 +/-& nbsp;0.3 nm are precipitated, which plays a major role in enhancing the hardness with the peak hardness of about 89.24 & PLUSMN; 3.77 HV. Er and Zr elements are proved to be an alternative way of the additive elements for developing a new 3D printing high-strength aluminum alloy.(C)& nbsp; 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：In2Se3 have attracted researcher's attention due to its potential optoelectronic and memory device applications, having various polymorphs with few of them having layered structure. There exists a non-layered phase with vacancy ordered in screw form known as gamma-In2Se3, whose properties are found to get affected majorly by the presence of defects. Here, the first principles calculations based on the density functional theory are performed to study the intrinsic point defects in defect wurtzite structure of gamma-In2Se3 using GGAPBE approximations. Thermodynamic charge transitions based on the formation energy of the defects are determined for all native defects, VIn, VSe, Ini, Sei, SeIn, InSe, under In-rich and Se-rich experimental growth conditions. The charge transition remains the same but transition energies differ for possible coordination of Se vacancies, whereas the charge transition as well as transition energy vary for different coordination sites of In vacancies. The In interstitial, Ini is the most favourable defect site under In-rich conditions whereas SeIn at the VBM and VIn1 near CBM are dominating under Se-rich conditions. The origin of n-type conductivity of gamma-In2Se3 is found to be the presence of Ini interstitials and InSe antisite in the defect wurtzite gamma-In2Se3. Further, the films grown using PLD shows an n-type conductivity under In-rich conditions leading to a good performance with photo responsivity and specific detectivity of 5.22 x 102 A/W and 5.08 x 1013 Jones. The understanding of these vacancies determines their thermodynamic behaviour which can help for the controlled growth of gamma-In2Se3 which leads to better device performance. (c) 2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Group 5 metals and their alloys are expected to become a new generation of hydrogen-permeable membranes to replace commercial palladium-based alloys. Recently, we synthesized a new Nb-Hf-Co alloy hydrogen permeation membrane, and the Nb30Hf35Co35 alloy has good mechanical properties and permeability. However, the development of alloys with higher hydrogen permeability is a challenge for these Nb-based membranes. To this end, Nb30Hf35Co35-xFex (0 < x < 35) alloys were developed and their microstructure and hydrogen permeation properties were systematically studied by means of SEM, XRD and TEM, among other techniques. When the Fe content is lower than 10 at%, Nb30Hf35Co35-xFex alloys are composed completely of a eutectic structure. With increasing Fe content, changes in microstructure and constituent phases are observed. In particular, a large amount of new impurity phases (Hf2Fe, Fe2Nb, FeNb and Fe0.7Hf0.3) is formed when the Fe content in the alloys is higher than 20 at%. With these changes, the hydrogen permeability (Phi) of these alloys first increases and then decreases. The Nb30Hf35Co30Fe5 alloy exhibits the largest hydrogen permeability at 673 K, at 3.41 x 10(-8) mol H-2 m(-1) s(-1) Pa-0.5, or 2.2 times that of palladium metal under the same conditions. The increase in the Phi value is mainly due to the increase in hydrogen diffusion coefficient (K) rather than hydrogen solubility (D). The present work demonstrates that Nb-Hf-Co-Fe quaternary alloys are expected to become a more promising hydrogen permeable material compared with traditional ternary alloys. (C)& nbsp;2022 Elsevier B.V. All rights reserved.
查看更多>>摘要：Directional solidified TiAl alloys have low density and good comprehensive high temperature performance, which is an ideal substitute material for high temperature structural parts. In this paper, phi 16.5 mm directional solidified Ti-45Al-5Nb sample with full-lamellar microstructure was prepared successfully by electromagnetic confinement technique at 10 mu m/s and relative tensile tests at 800 degrees C were also performed. The tensile strength of Ti-45Al-5Nb alloy at 800 degrees C is 765 MPa and the elongation is 16%. Moreover, results of tensile process characteristics and fracture analysis show that this material has two distinct fracture mechanisms at 800 degrees C, which are cleavage fracture mechanism and microporous aggregation fracture mechanism. Two fracture mechanisms do not exist at the same time, and for a particular specimen, the fracture process is dominated by only one of them. Different fracture mechanisms are determined by the lamellar orientation difference and element segregation. When the orientation of adjacent grains is similar and the segregation is light, the fracture process is dominated by the cleavage fracture mechanism. Otherwise, proportion and scale of the gamma phase at the grain boundary increase and the B2 phase is generated. In this case, the microporous aggregation fracture mechanism will dominate the fracture process. (c) 2022 Elsevier B.V. All rights reserved.
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